Well logging scintillation detectors use nuclear sources and shields below a crystal which emits light in response to gamma radiation. The light is sensed by a photomultiplier tube which produces signals which are amplified and transmitted to electrical interpreting equipment above the surface.
Problems exist that crystals are subject to breakage, and that the system over time loses efficiency.
The well logging equipment is lowered at rapid speeds into deep wells. Pumping wells produces shocks, which may fracture the crystal or interfere with optical transmission. Cracked crystals, while they may still create light upon experiencing gamma radiation, produce less light entering the photomultiplier tube because the cracks reflect the light back into the crystal.
The well logging scintillation detectors are used at substantial well depths, and thus are subject to increased atmospheres of pressure. Speeds at which the detectors traverse the wells further add pressure differential and variance. As a result, over time, the detector's output denigrates and the detectors have to be replaced.
High well temperature also results in signal degradation. At elevated temperatures the photomultiplier produced random output pulses in the absence of incident light. The current produced by these pulses is called "dark current" and its average magnitude increases with the temperature.
The temperature effects on the scintillation events, which are caused by the incident radiation with constant energy, may result in a decrease in amplitude and an increase in duration as the temperature increases. That results in less accurate measurement of the intensity of the incident radiation, and errors in soil composition analysis.
Problems continue to exist in the cracking of crystals and in temperature-related reduced efficiency of crystals which are not cracked.